docs: def _get_v1(self, imt):
          """
          Calculates Bradley's V1 term. Equation 2 (page 1814) and 6 (page 1816)
          based on SA period
          """
  
          if imt == PGA():
              v1 = 1800.
  
          else:
              T = imt.period
              v1a = np.clip((1130 * (T / 0.75)**-0.11), 1130, np.inf)
              v1 = np.clip(v1a, -np.inf, 1800.)
  
          return v1